Southern IPM blog posts

Funded by USDA National Institute of Food and Agriculture

The Southern Region IPM Center is located at North Carolina State University, 1730 Varsity Drive, Suite 110, Raleigh, NC 27606, and is sponsored by the United States Department of Agriculture, National Institute of Food and Agriculture.

Continuing with excerpts from my testimony before the Arkansas Joint Agriculture, Forestry and Economic Development Committee meeting on dicamba, I will focus on what is required to get a large acreage or a landscape effect from a herbicide.

This effect occurred in the high use areas in west Tennessee, northeast Arkansas, the Mississippi Delta, and the Missouri Bootheel. It is much different than what is happening in areas or states where less dicamba is being applied. In these high use areas, about two to three weeks after the drift and volatility patterns that I described appeared, the bomb went off — both in 2016 and to a much greater extent in 2017.

When that happened, there were multi-county areas in each state where every acre of non-dicamba-tolerant soybeans were affected. Almost every soybean plant at a similar growth stage was expressing a similar degree of symptoms, and the injury was perfectly uniform across every field. The patterns from earlier drift and/or volatility were completely masked by this uniform effect.

What does it take to cause this uniform landscape effect to occur?

First it takes ultra-sensitive plant species to a given herbicide because the dose rates occurring are extremely low.

Then, the herbicide must be uniformly distributed over this landscape area at a fairly uniform dose rate. This does not happen by blowing spray droplets, herbicide crystals or volatiles in the wind. When these are being blown across the soil or crop surface by wind, patterns are obvious and they do not blow long distances before dilution, turbulence and thermal mixing take them out — that is, they just blow away.